Robin DiFrancesco

Inhibition of Atazanavir Oral Absorption by Lansoprazole Gastric Acid Suppression in Healthy Volunteers

Study Objective. To determine whether the pharmacokinetics of atazanavir, a protease inhibitor used to treat human immunodeficiency virus (HIV) infection, are altered by its coadministration with lansoprazole, a proton pump inhibitor.

Quality assurance program for Clinical measurement of antiretrovirals: AIDS Clinical Trials Group proficiency testing program for pediatric and adult pharmacology Laboratories

ABSTRACT Clinical trials designed to compare antiretroviral regimens, investigate therapeutic drug monitoring, or measure pharmacometrics often include protease inhibitors (PIs), nonnucleoside reverse transcriptase inhibitors (NNRTIs), and nucleoside reverse transcriptase inhibitors, requiring the measurement of these antiretrovirals in plasma. Within the adult and pediatric AIDS Clinical Trials Group (ACTG), a network of Pharmacology Support Laboratories (PSLs) is a component of the group laboratory infrastructure and conducts these types of pharmacologic assays. The adult ACTG has developed a comprehensive quality assurance program for the conduct of clinical pharmacology protocols, one component of which is the antiretroviral proficiency testing (PT) program that has been implemented between the adult and pediatric pharmacology laboratories of the ACTG. PT testing samples were prepared and distributed in July 2001, February 2002, and July 2002. High, medium, and low concentrations of PIs (indinavir, saquinavir, amprenavir, lopinavir, ritonavir, and nelfinavir) and NNRTIs (nevirapine and efavirenz) were added to drug-free EDTA plasma and distributed, on dry ice, to eight ACTG PSLs. One testing laboratory used liquid chromatography-tandem mass spectrometry, and seven used high-performance liquid chromatography-UV analysis. A result was considered acceptable if it was within 20% deviation of the assigned concentration. For all concentrations of PIs evaluated, 96% of samples tested (430 of 448 measurements) met the acceptance criteria. For both NNRTIs, 100% of samples tested (140 of 140 measurements) met the acceptance criteria. In conclusion, the PT program results presented demonstrate excellent interlaboratory agreement for all antiretrovirals tested and provide support for the merger of plasma concentration data among laboratories for large clinical trials.

Determination of protease inhibitors using liquid chromatography-tandem mass spectrometry.

A method for the analysis of six protease inhibitors and one metabolite has been developed and validated. Amprenavir, ritonavir, saquinavir, lopinavir, indinavir, nelfinavir, and an active metabolite of nelfinavir (M8) are quantitated using reversed-phase liquid chromatography coupled to tandem mass spectrometry, equipped with an electrospray ionization source (ESI-LC-MS-MS). The validation data presented here shows that the method allows the rugged analysis of these species from one aliquot. The evolution of complex drug interactions assessments and the clinical use of therapeutic drug monitoring for these antiretrovirals will be a potential immediate application of this method.

Quality assurance program for pharmacokinetic assay of antiretrovirals : ACTG proficiency testing for pediatric and adult pharmacology support laboratories, 2003 to 2004 A requirement for therapeutic drug monitoring

Proficiency testing (PT) is a mandated requirement for clinical laboratories doing therapeutic drug monitoring and is an invaluable tool to help laboratories identify and correct problems in analytical procedures. The AIDS Clinical Trial Group Pharmacology Quality Assurance Committee implemented a new antiretroviral PT program for all currently available antiretroviral drugs in 2001. The PT program was designed for the AIDS Clinical Trial Group Pharmacology Specialty Laboratories actively involved in assaying these drugs in clinical trial samples so as to comply with the Clinical Laboratory Improvement Amendments. Results from the first 3 rounds of PT have been analyzed and reported1 and provided support for formalizing the guidelines of the PT testing program. The PT program has expanded with the addition of nucleoside reverse transcription inhibitors (NRTIs) and atazanavir. This report includes results from rounds 4 to 7 over 2 additional years of standard operations. Additionally we include results from NRTIs for all rounds and atazanavir for a single round. There were 9 participating laboratories. Eight used high-performance liquid chromatography as the primary method of detection and 2/8 also reported LC-MS-MS results. One laboratory used LC-MS-MS as their primary detection method. All laboratories measured protease inhibitors, most measured at least 1 non-nucleoside reverse transcription inhibitor and 5 had NRTI capabilities. Results were normally distributed and the acceptance range of ±20% best corresponded to a 95% confidence interval. Overall score for 9 participating laboratories was 96% correct out of 1826 challenges over 4 rounds. Laboratories scored 95, 98 and 97% correct for protease inhibitors, non-nucleoside reverse transcription inhibitorss and NRTIs, respectively. Three laboratories reporting LC-MS-MS results had 92% correct (347/378) challenges for all drugs. The percentage of correct results is about the same as previously reported1. There is a continued need for a PT program to help participating laboratories maintain essential quality assurance and quality control.

Multidrug resistance 1 polymorphisms and trough concentrations of atazanavir and lopinavir in patients with HIV

INTRODUCTION HIV-infected patients receiving protease inhibitors may benefit from therapeutic drug monitoring-assisted dose adjustment to achieve target plasma concentrations. However, efflux pumps such as permeability-glycoprotein, which is encoded by the multidrug resistance (MDR)1 gene, may decrease intracellular drug concentrations, thus reducing the amount of drug at the site of action. Plasma concentrations of protease inhibitors and CD4 cell count response have been associated with the T allele at the MDR1 C3435T locus. We examined MDR1 single nucleotide polymorphisms in a cohort of patients in whom therapeutic drug monitoring is ongoing through a research protocol. METHODS In a multicenter study, genotypic analyses at two MDR1 loci, C3435T and G2677T, were performed by a real-time polymerase chain reaction method using DNA from 103 patients categorized as substance users or nonusers on atazanavir or lopinavir as the primary antiretrovirals. Allelic frequencies were determined as a function of racial/ethnic background, substance use status and trough concentrations of atazanavir and lopinavir. RESULTS The C/T and G/T alleles at the MDR1 C3435T and G2677T loci were equally frequent in the Caucasian population, but the wild-type alleles were more prevalent in the African-American population (59% homozygous [CC] and 32% heterozygous [CT] for C3435T; 80% homozygous [GG] and 16% heterozygous [GT] for G2677T). The frequencies in the Hispanic population were 46% CC and 38% CT for C3435T, and 58% GG and 38% GT for G2677T. No significant differences were seen in allele frequencies for MDR1 polymorphisms in substance user versus nonuser groups. Trough plasma concentrations of atazanavir or lopinavir were not correlated with the variant T allele. CONCLUSIONS These data confirm the higher prevalence of wild-type alleles of the MDR1 gene in African-Americans and the linkage disequilibrium between C3435T and G2677T loci. The T allele at the MDR1 C3435T and G2677T loci was not associated with higher atazanavir or lopinavir trough concentrations.

Clinical Pharmacology Quality Assurance for HIV and Related Infectious Diseases Research

The global HIV epidemic continues to grow in certain regions while contracting in others, necessitating a broadened research agenda, including clinical pharmacology of tuberculosis, hepatitis, malaria, and immune activation/inflammation, underscoring the need for a coordinated quality assurance approach. A comprehensive program has been developed and implemented by the University at Buffalo HIV Clinical Pharmacology Quality Assurance and Quality Control Program, funded by the National Institutes of Health.

Effects of Grapefruit Juice on Pharmacokinetic Exposure to Indinavir in HIV‐Positive Subjects

The objective of this study was to determine the effects of double‐strength grapefruit juice on gastric pH and systemic bioavailability of indinavir in HIV‐infected subjects receiving indinavir. Fourteen HIV‐infected subjects took 800 mg of indinavir with 6 ounces (180 ml) of water or double‐strength grapefruit juice. Gastric pH was measured and blood samples were collected for 5 hours after indinavir dosing. Grapefruit juice increased the mean gastric pH (from 1.39 ± 0.4 to 3.20 ± 0.3; p < 0.05) and slightly delayed the absorption of indinavir (tmax increased from 1.12 ± 0.8hto 1.56± 0.6 h; p < 0.05). However, there were no significant differences in indinavir exposure. Cmax was 16.7 ± 7.3 μ with water versus 13.9 ± 4.2 μ with grapefruit juice (p = NS), and AUC0–8 was 37.5 ± 19 with water versus 36.9 ± 15 with grapefruit juice (p = NS). The authors concluded that concomitant administration of grapefruit juice increases gastric pH and delays indinavir absorption but does not uniformly affect the systemic bioavailability of indinavir in HIV‐infected subjects.

The Effects of Once‐Daily Saquinavir/Minidose Ritonavir on the Pharmacokinetics of Methadone

Twelve methadone‐maintained HIV‐negative subjects were given saquinavir/ritonavir (SQV/rtv) 1600 mg/100 mg once daily for 14 days. Pharmacokinetic evaluations of total and unbound methadone enantiomers (R and S) were conducted before and after SQV/rtv. SQV/rtv was well tolerated, with no ACTG Grade 3–4 adverse events, no evidence of sedation, and no changes in methadone dose. For R‐methadone (active isomer), Cmax, AUC0–24 h, and Cmin were unchanged, but percent unbound 4 hours after dosing was reduced by 12%. For S‐methadone, no differences in pharmacokinetic parameters of total drug were seen, but unbound concentrations were reduced by 15% and 21% at 4 and 24 hours after dosing, respectively. SQV trough concentrations exceeded the anticipated EC50 (50 ng/mL) in 10/12 subjects, persisting for at least 6 hours after the final dose in 4/6 subjects. Once‐daily SQV/rtv in methadone‐maintained subjects is safe and not associated with any clinically significant interaction with methadone during 14 days of concomitant administration.

Low-Frequency Nevirapine (NVP)–Resistant HIV-1 Variants Are Not Associated With Failure of Antiretroviral Therapy in Women Without Prior Exposure to Single-Dose NVP

BACKGROUND Low-frequency nevirapine (NVP)-resistant variants have been associated with virologic failure (VF) of initial NVP-based combination antiretroviral therapy (cART) in women with prior exposure to single-dose NVP (sdNVP). We investigated whether a similar association exists in women without prior sdNVP exposure. METHODS Pre-cART plasma was analyzed by allele-specific polymerase chain reaction to quantify NVP-resistant mutants in human immunodeficiency virus-infected African women without prior sdNVP who were starting first-line NVP-based cART in the OCTANE/A5208 trial 2. Associations between NVP-resistant mutants and VF or death were determined and compared with published results from women participating in the OCTANE/A5208 trial 1 who had taken sdNVP and initiated NVP-based cART. RESULTS Pre-cART NVP-resistant variants were detected in 18% (39/219) of women without prior sdNVP exposure, compared to 45% (51/114) with prior sdNVP exposure (P < .001). Among women without prior sdNVP exposure, 8 of 39 (21%) with NVP-resistant variants experienced VF or death vs 31 of 180 (17%) without such variants (P = .65); this compares with 21 of 51 (41%) vs 9 of 63 (14%) among women with prior exposure (P = .001). CONCLUSIONS The risk of VF on NVP-based cART from NVP-resistant variants differs between sdNVP-exposed and -unexposed women. This difference may be driven by drug-resistance mutations emerging after sdNVP exposure that are linked on the same viral genome. CLINICAL TRIALS REGISTRATION NCT00089505.

Mycophenolic Acid Pharmacokinetics During Maintenance Immunosuppression in African American and Caucasian Renal Transplant Recipients

Renal transplant recipients exhibit variability in mycophenolic acid (MPA) and MPA glucuronide (MPAG) pharmacokinetics, which are influenced by clinical and demographic factors. Racial influence on MPA and MPAG pharmacokinetics was investigated in 53 patients: 17 African American males, 22 Caucasian males, and 14 females receiving mycophenolate mofetil (MMF) and cyclosporine. A 12‐hour steady‐state pharmacokinetic study was conducted. Enterohepatic circulation of MPA was characterized by a second plasma concentration peak and was included in a novel statistical model with MPAG. MPA clearance in African American males was 26.5 ± 14.4 L/h versus 17.9 ± 6.1 L/h in Caucasian males (P = .035) and 16.1 ± 4.6 L/h in Caucasian females (P = .024) with no difference noted in MPA troughs. Enterohepatic circulation occurred less frequently in African American males (23%) compared with Caucasian males (42%) and Caucasian females (50%) (P > .05). Cyclosporine exposure was correlated with MPA and MPAG pharmacokinetics, whereas creatinine clearance influenced MPAG pharmacokinetics. A racial difference was noted with more rapid MPA clearance in African American males compared with Caucasians. The results support differential MPA dosing and the role of therapeutic drug monitoring in addition to considering the influence of renal function and concurrent immunosuppressives on MPA and MPAG pharmacokinetics.